Chemical and physical passivation of type II strained-layer superlattice devices by means of thiolated self-assembled monolayers and polymer encapsulates

• Type II superlattice detectors were passivated using various thiolated monolayers as well as polymers.
• XPS conducted on hexanethiol, dodecanethiol, octadecanethiol, and cysteamine deposited on InAs, GaSb, and InSb wafers.
• DFT modeling was performed on the adhesion of cysteamine onto (1 1 0) InAs.
• Dark Current reduction through passivation of p-type type II superlattice detectors with thiolated monolayers and polymers.

The efficacy of solution deposition of thiolated self-assembled monolayers (SAMs) has been explored for the purpose of passivating III–V type II superlattice (T2SL) photodetectors, more specifically a p-type heterojunction device. Sulfur passivation has previously been achieved on T2SL devices. However, degradation over time, temperature sensitivity and inconsistent reproducibility necessitate a physical encapsulate that can chemically bond to the chemical passivant. Thus, this research investigates two passivation methods, surface passivation with a thiol monolayer and passivation with a polymer encapsulant with a view toward future combination of these techniques. Analysis of the physical and chemical condition of the surface prior to deposition assisted in the development of ideal processes for optimized film quality. Successful deposition was facilitated by in situ oxide removal. Various commercially available functional (cysteamine) and non-functional (alkane) thiolated monolayers were investigated. Dark current was reduced by 3 orders of magnitude and achieved negligible surface leakage at low bias levels. The lowest dark current result, 7.69 × 10−6 A/cm2 at 50 mV, was achieved through passivation with cysteamine.